All about contact lenses

• Contact lenses sit on the cornea (clear dome at the front of the eye) and offer an alternative option to spectacles for correcting vision.
• Contact lenses are manufactured in rigid (hard) or soft forms from specially designed oxygen permeable materials.
• Rigid lenses can often last beyond 1 year. Soft lenses are replaced more frequently, usually supplied as daily, two-weekly or monthly disposable.
• All contact lenses, except daily disposables, need to be cleaned and then stored in fresh contact lens disinfecting solution in a contact lens case.
• Both rigid and soft contact lenses can be safe to wear when used properly and under the supervision of an optometrist or eye doctor.
• Special types of soft contact lenses and ortho-k have evidence to slow myopia progression in children, especially those aged 6-16 years.

Contact lenses offer an alternative option to spectacles for correcting vision and are typically worn for one of three reasons.

1. To correct vision as an alternative to glasses, for functional or aesthetic reasons such as to play sport.¹
2. To correct vision where glasses are not an option, for example in people with very high prescriptions or for people with irregular eye shapes like keratoconus.¹
3. They are sometimes prescribed for medical conditions of the eye, to promote healing of the eye surface.²

Because contact lenses sit on the surface of the eye, and move with the eye, they offer a more natural way to correct vision than glasses. They are less cumbersome than glasses, far less susceptible to falling off, and offer a full view of the world unrestricted by glasses frames.

The smallest contact lenses start at around 8mm in diameter, are made from a stiff 'rigid' material, and are designed to fit to snugly on the cornea (the clear dome at the front of the eye). Rigid corneal lenses are mostly worn during the day only. They were more popular in the past before soft contact lens materials were developed but are now mostly worn for special purposes such as more complex prescriptions.

Rigid contact lens types are the most durable and with good care can last up to a few years, although more frequent replacement has been recommended to avoid possible complications from lens condition deteriorating over time.¹

Ortho-k lenses are a special type of rigid contact lens that are worn during sleep when they gently flatten the cornea to create a temporary way of correcting vision that is reversed when wear is stopped. They are typically around 10-11mm in size.

Soft contact lenses are bigger than rigid corneal lenses as they are designed to fit over the entire cornea and just onto the white of the eye. They are typically 13-14mm in diameter. They are less durable than rigid lenses, which has led to them mostly being supplied in disposable format, either to be worn just for the day and then thrown away, or the same lens kept for up to a month with overnight cleaning and storage in contact lens disinfection solutions.

The largest type of contact lenses are called scleral lenses because they are fit to extend further onto the white of the eye which is called the sclera. These can be 15-22mm in diameter. Scleral lenses are mainly fit for more complex prescriptions and cosmetic reasons.

Modern contact lenses are made from specialized clear plastics that are permeable to allow oxygen to flow through to the eye, allowing them to give similar health effect to not wearing contact lenses.³

Most rigid (hard) lens types are made from a small button of lens material that is sculpted into shape on a specialized computer control lathe to 1 micron precision. That's 0.001mm precision, so highly precise.

Soft lenses can be lathed like rigid lenses, but most are molded into shape using sophisticated specially designed equipment. Molding is much faster than lathing, which allows more lenses to be made in a shorter period of time, and enabled manufactures to provide disposable soft lens options.

Daily replacement has become the most common form of soft contact lens supply - if a rigid lens were to be worn every day and last 1 year, then the equivalent for daily disposable soft lenses would require 365 lenses. This alone shows how efficient molded soft contact lens production has become in comparison to manufacture of individually made rigid lenses.

Regardless of type, all contact lenses should be fit by an optometrist, eye doctor, or a professional who is trained and qualified to fit contact lenses, and this is particularly important for children and teenagers. Poorly fitted rigid lenses will likely be uncomfortable and could cause damage. Ortho-k lenses especially require accurate measurements to fit to ensure they fully correct vision.^1,4

Rigid lenses are the most complex to fit as they need to be aligned closely with the surface of the eye to avoid discomfort. The eye doctor will measure the curvature of the front surface of the eye, and then use these measurements to design and order a custom fit lens. In some cases they may try lenses selected from a trial set to assist the lens design process, much like a jeweler may use a finger size gauge to find the perfectly fitting ring.

Soft lenses are much more flexible, which allows them to more easily match the shape of the eye. This makes them easier to fit, but they still require professional assessment to ensure optimal lens fit is achieved. Unlike rigid and ortho-k lenses, that most likely need to be specially designed and ordered, most disposable soft lenses are pre-packaged which generally makes for quicker supply.

Before taking contact lenses home you should be shown how to apply and remove the lenses, and if daily disposable, how to clean and store them while not being worn. It's important that these steps are always followed to keep lenses in optimal condition and reduce risk of infection.¹

Eyes are very sensitive - most people would have experienced getting some dust or an eyelash in their eye to realize how uncomfortable it feels. Fortunately, because they are fit to match the same shape as your eye, contact lenses do not have the same effect. Once someone is adapted to contact lenses, most of the time they aren't aware of them being on their eyes.

There is a big difference in comfort between rigid and soft contact lenses, and a fair analogy to keep in mind is to think of rigid lenses like stiff work boots and soft lenses as like indoor slippers. Rigid contact lenses are often uncomfortable at the start, but become more comfortable with time to the point where they are not noticeable. Soft lenses on the other hand are more comfortable at outset but like slippers are less durable and need to be replaced more frequently.

Soft lenses have become the most popular option, mainly because to start with they are more comfortable to wear, and easier to fit, but they need to be replaced more regularly than rigid lenses.¹

All contact lenses, except for daily disposables, need to be cleaned and then stored in fresh contact lens disinfecting solution in a contact lens case. It's vital that only proper contact lens solutions are used for cleaning and disinfecting contact lenses and that the case is replaced regularly,¹ ideally every time a new bottle of disinfecting solution is started or at the most every 3-months.

Contact lens cleaning and disinfection is important to keep the lenses clean, and also to reduce risk of contact lens related eye infection. It is also important to avoid tap water coming into contact with contact lenses or contact lens accessories like cases. This is because there is a rare but potentially sight threatening eye infection called acanthamoeba keratitis that is linked to water contamination of contact lenses.⁵

Both rigid and soft contact lenses can be safe to wear when used properly and under the supervision of an optometrist or eye doctor. Research shows that daily disposables worn only during the day are the safest and healthiest type of soft contact lens.⁶

Overnight wear of any type of soft contact lens dramatically increases the risk of eye health problems and eye infection, making overnight wear rarely recommended.¹ Ortho-k lenses are worn overnight, but have a better safety profile because they are a rigid type of contact lens that provides more oxygen permeability to the eye than soft contact lenses.^7,8 They are also removed during waking hours, giving the eyelids and eye surface a break from the contact lens, unlike soft contact lenses worn day-and-night.

The safety of ortho-k has been reported to be similar to that of reusable soft contact lenses.^6-8

Interestingly, children aged 8-12 appear to be safer soft contact lens wearers than teenagers,⁹ likely due to better adherence to lens handling processes and closer supervision of their contact lens wear by parents.

Yes, children and teens can safely wear all types of contact lenses as long as they are comfortable to apply and remove them, and able to accurately follow lens care instructions. In fact contact lenses have been shown to make them feel more confident and able to participate in school and sport compared to wearing glasses.¹⁰

A further benefit is that specially designed myopia control soft contact lenses and orthokeratology have been shown to be effecting in slowing myopia progression in children and teens,¹¹ which gives them clearer vision between eye exams and better long-term eye health as well.

The ideal option for your child or teenager will depend on their prescription, eye health and other factors such as sports, hobbies and daily activities. Your optometrist or eye doctor will discuss these options with you.

Here are some examples of how your child’s individual situation can help point towards the most suitable contact lens option for them.

• Daily disposable contact lenses are the safest type of contact lenses to wear⁶ but not all prescriptions are suitable for them.¹
• Reusable contact lenses can offer a wider availability and suitability for higher prescriptions than daily disposable or ortho-k contact lenses¹
• Ortho-k provides the freedom for your child to see clearly during waking hours without needing to wear any spectacles or contact lenses.⁴
• If your child does swimming or water sports, ortho-k is the safest way to correct their vision without glasses,⁴ as it avoids water exposure to contact lenses which is a key risk factor for serious eye infection.⁵
• If you, as the parent, wish to have closer supervision over all contact lens wearing time, ortho-k can be ideal as all wearing time occurs at home, overnight.⁴
• If your child lives between two households and/or travels a lot, daily disposable soft contact lenses can be ideal as handling is simple and multiple lenses can be kept in various locations.

Your child’s eye care practitioner or eye doctor (optician, optometrist or ophthalmologist) may use the following Infographic from MyopiaProfile.com to illustrate the benefits and safety of contact lens wear in children and teenagers. We developed the Infographics because using pictures in health communications has been shown to improve learning and application of advice between health professionals, patients and their parents or carers.¹² 

This is part of a set of four infographic panels which describe visual environment advice, treatment options, contact lens wear in kids, and why myopia management is essential. 

1. Wolffsohn JS, Dumbleton K, Huntjens B, Kandel H, Koh S, Kunnen CME, Nagra M, Pult H, Sulley AL, Vianya-Estopa M, Walsh K, Wong S, Stapleton F. CLEAR - Evidence-based contact lens practice. Cont Lens Anterior Eye. 2021 Apr;44(2):368-397.
2. Jacobs DS, Carrasquillo KG, Cottrell PD, Fernández-Velázquez FJ, Gil-Cazorla R, Jalbert I, Pucker AD, Riccobono K, Robertson DM, Szczotka-Flynn L, Speedwell L, Stapleton F. CLEAR - Medical use of contact lenses. Cont Lens Anterior Eye. 2021 Apr;44(2):289-329.
3. Morgan PB, Murphy PJ, Gifford KL, Gifford P, Golebiowski B, Johnson L, Makrynioti D, Moezzi AM, Moody K, Navascues-Cornago M, Schweizer H, Swiderska K, Young G, Willcox M. CLEAR - Effect of contact lens materials and designs on the anatomy and physiology of the eye. Cont Lens Anterior Eye. 2021 Apr;44(2):192-219. 
4. Vincent SJ, Cho P, Chan KY, Fadel D, Ghorbani-Mojarrad N, González-Méijome JM, Johnson L, Kang P, Michaud L, Simard P, Jones L. CLEAR - Orthokeratology. Cont Lens Anterior Eye. 2021 Apr;44(2):240-269. 
5. Ibrahim YW, Boase DL, Cree IA. How Could Contact Lens Wearers Be at Risk of Acanthamoeba Infection? A Review. J Optom. 2009;2(2):60–6. (link)
6. Stapleton F, Keay L, Edwards K, Naduvilath T, Dart JK, Brian G, Holden BA. The incidence of contact lens-related microbial keratitis in Australia. Ophthalmology. 2008 Oct;115(10):1655-62.
7. Bullimore MA, Sinnott LT, Jones-Jordan LA. The risk of microbial keratitis with overnight corneal reshaping lenses. Optom Vis Sci. 2013 Sep;90(9):937-44
8. Bullimore MA, Mirsayafov DS, Khurai AR, Kononov LB, Asatrian SP, Shmakov AN, Richdale K, Gorev VV. Pediatric Microbial Keratitis With Overnight Orthokeratology in Russia. Eye Contact Lens. 2021 Jul 1;47(7):420-425.
9. Bullimore MA. The Safety of Soft Contact Lenses in Children. Optom Vis Sci. 2017 Jun;94(6):638-646. 
10. Walline JJ, Gaume A, Jones LA, Rah MJ, Manny RE, Berntsen DA, Chitkara M, Kim A, Quinn N. Benefits of contact lens wear for children and teens. Eye Contact Lens. 2007;33(6 Pt 1):317-321. 
11. Brennan NA, Toubouti YM, Cheng X, Bullimore MA. Efficacy in myopia control. Prog Retin Eye Res. 2021 Jul;83:100923.
12. Houts PS, Doak CC, Doak LG, Loscalzo MJ. The role of pictures in improving health communication: A review of research on attention, comprehension, recall, and adherence. Patient Education and Counseling. 2006;61:173-90.